Dental radiology apparatus and signal processing method used therewith

ABSTRACT

A dental radiology apparatus having: an intraoral sensor comprising a detector including an active pixel array produced using biCMOS technology and converting a received x-ray into at least one analog electrical output signal; an electronic module encapsulated in a case and which has at least one detector activation device, the module linked to the sensor for the transmission to the sensor of a detector activation signal generated in the module and for the transmission to the module of the at least one analog electrical output signal, the module having analog-digital means for converting the at least one analog electrical output signal into at least one digital output signal. A remote processing and display unit of the at least one digital output signal is linked to the electronic module to ensure the transmission to the unit of the at least one digital output signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation of U.S. Ser. No. 13/188,497 titled DENTALRADIOLOGY APPARATUS AND SIGNAL PROCESSING METHOD USED THEREWITH filed onJul. 22, 2011 now U.S. Pat. No. 8,319,190 in the names of Boucly et al,which was a Continuation of U.S. Ser. No. 12/505,556 titled DENTALRADIOLOGY APPARATUS AND SIGNAL PROCESSING METHOD USED THEREWITH filed onJul. 20, 2009 in the names of Boucly et al, which issued as U.S. Pat.No. 8,008,628, which was a Divisional application of U.S. Ser. No.10/580,395 titled DENTAL RADIOLOGY APPARATUS AND SIGNAL PROCESSINGMETHOD USED THEREWITH filed on Apr. 27, 2007 in the names of Boucly etal, which issued as U.S. Pat. No. 7,608,834, which claims priority toPCT/EP2004/012885 filed on Nov. 13, 2004, which claims priority to EP03292901.0 filed Nov. 21, 2003.

FIELD OF THE INVENTION

The invention relates to the field of dental radiology.

BACKGROUND OF THE INVENTION

Dental radiology equipment as described in French patent FR 2,547,495and European patent No. 0,129,451 is known.

Such equipment comprises an x-ray source that emits radiation directedto a tooth located in a patient's mouth and behind which is an intraoralsensor that receives the x-rays that have passed through the tooth.

This sensor comprises: a scintillator on entry to convert the x-raysthat have passed through the tooth into visible light; and a fiber opticplate to transmit the converted visible light to a charge-coupled deviceCCD-type detector, which converts the converted visible light into ananalog electrical signal, while absorbing the residual x-rays that havenot been converted into visible light.

The electrical signal is amplified and transmitted in analog formthrough a long cable, to a remote processing and display workstationwhere the signal is digitized and processed to produce an image that isthen viewed on a display screen.

This type of equipment with a charge-coupled device detector creates ahigh signal-to-noise ratio (SNR), for example, of about 60 dB.

Also known, according to U.S. Pat. No. 5,912,942, is a type of x-raydetector wherein the active pixel sensor (APS) uses CMOS manufacturingtechnology.

In the above-mentioned patent, the radiology equipment described thereincomprises: a source of x-rays passing through an object, a scintillatorthat converts the x-rays that have passed through the object intovisible light, and a fiber optic plate that transmits the convertedvisible light to an active pixels array that converts it into an analogelectrical signal.

It can be observed that the CMOS detector obtains a signal-to-noiseratio (SNR) of inferior quality to that of the CCD detector.

Several factors have thus been identified that limit the signal-to-noiseratio of the CMOS detector.

Among these factors, is the dark current that can be defined as beingthe electrical current collected at the detector output when the latteris not exposed to any x-ray.

The presence of the dark current leads to a deterioration of thesignal-to-noise ratio.

It may be noted that, insofar as the intensity of the dark current hasthe special feature of considerably increasing with temperature and asthe detector heats during its use, it is advisable to cool it and/or notoperate it for too long a period so as not to further deteriorate thesignal-to-noise ratio.

A second limiting factor is the detector's fill factor.

For a CCD detector, the fill factor is in theory 1, which means that thewhole pixel surface is used to capture the x-rays and produce thecorresponding electrical charge that will contribute to forming theimage of the x-rayed tooth.

On the contrary, in a CMOS active pixel detector, the active element ofthe pixel occupies part of the pixel surface, without howevercontributing to the capture of the x-ray.

With part of the pixel not contributing to the fill, i.e. notcontributing to the photon-electron conversion, the fill factor is lessthan 1, which hinders obtaining a good signal-to-noise ratio.

A third limiting factor results from the fact that today we do not knowhow to use CMOS technology to make large size monolithic active pixelarrays, typically about 20×30 mm, which are the commonly used dimensionsfor dental radiology sensors.

To obtain a large-size active pixel array in CMOS technology, it isnecessary to assemble together several smaller-size sub-arrays by“stitching”.

The unevenness created by an array obtained in this way contributes todeteriorating the signal-to-noise ratio.

Further, it should be noted that the conditions specific to the field ofdental radiology make the design of dental radiology apparatus with ahigh quality signal-to-noise ratio particularly difficult.

In particular, insofar as people are exposed to x-rays, the x-ray dosesused should be as low as possible and these people should be exposed tothe x-rays for the shortest possible time.

In other fields where a CMOS technology x-ray detector is used, thex-ray doses are not required to be as low as in dental radiology, whichenables a higher intensity signal at the detector output, and thus abetter signal-to-noise ratio.

Also, one of the special features of intraoral dental radiology sensorsstems from the fact that the sensor that is placed in a patient's mouthhas to be as small as possible to limit the discomfort caused to thepatient, which implies reducing the number of components in the sensor.

It may be noted that, in a preferred embodiment of the x-ray detectorsdescribed in U.S. Pat. No. 5,912,942, the sensor comprises an integralanalog-digital converter in order to digitize the analog output signalthat is to be transmitted to the remote computer without delay.

Detector design like this goes against the miniaturization required forinstallation in a patient's mouth.

In addition, the introduction of an analog-digital converter alongside aCMOS technology active pixel array, which is an analog element,constitutes an additional source of noise which, added to the constraintof a minimal dose of x-rays, contributes to deteriorating the detector'ssignal-to-noise ratio.

Other unmentioned sources of noise may be noted that are also capable ofaffecting the detector's signal-to-noise ratio.

Generally, there is a need for new dental radiology apparatuses andsignal processing methods used therein, which can improve thesignal-to-noise ratio provided by the apparatus's detector.

It is also apparent that the use of existing dental radiologyapparatuses causes hygiene problems that it would be desirable to solve,at least to some extent.

Thus, when the dentist wearing surgical gloves places an intraoralsensor behind a tooth in a patient's mouth, said sensor comprising oneof the detector types mentioned above, he/she has to switch on thesensor and then start the x-ray generator.

To do this, he/she has to go to the computer located a few meters away,which is already not very practical, and then click on a computer mouseto start the sensor and the x-ray generator by means of a programmedinterface.

However, at this time, the dentist is wearing gloves that are alreadycontaminated by the patient's saliva, which risks causingcross-contamination when the dentist later handles the computer mouseusing gloves impregnated with another patient's saliva.

Faced with such a situation, the dentist has then either to remove thegloves before handling the mouse, or disinfect them after use, which inboth cases represents additional constraints that quickly become onerouswhen they are repeated several dozen times a day.

On the other hand, there is also a need to have dental radiologyapparatus as small as possible, especially for the intraoral sensor andrelated electronics.

Thus the invention aims to remedy at least one of the above-mentionedproblems.

SUMMARY OF THE INVENTION

According to a first aspect, the invention relates to a dental radiologyapparatus, characterized in that it comprises: an intraoral sensorcomprising a detector that includes an active pixel array produced usingbiCMOS technology and converting received x-rays into at least oneanalog electrical output signal, an electronic module encapsulated in acase and which comprises at least one detector activation device, themodule being linked to the sensor by a wire link for the transmission tosaid sensor of a detector activation signal generated in the module andfor the transmission to the module of said at least one analogelectrical output signal, the module having analog-digital means ofconversion of said at least one analog electrical output signal into atleast one digital output signal, and a remote processing and displayunit of said at least one digital output signal which is linked to theelectronic module by a wire link intended to ensure the transmission tothe unit of said at least one digital output signal.

According to this aspect of the invention, the electronic module has atleast one detector activation device and is sufficiently close to thesensor to be handled by a dentist during the intervention with a patientand thus enable, by using the activation device by hand, or with a footif the module is located on the floor, the sensor to be switched on forthe purpose of taking an image of a tooth.

Insofar as the electronic module equipped with the activation device islocated within the dentist's sphere of activity, this saves him/her fromhaving to move as far as the processing and display unit which inpractice is several meters away from said dentist.

Similarly, this precludes the problems of cross-contamination that mayarise if the dentist has to move as far as the remote processing anddisplay unit to handle a sensor activation device such as a computermouse by means of a programmed interface.

Assuming the computer mouse has to be disinfected, this additionaldisinfection operation is also avoided.

Further, the nearness of the electronic module to the sensor means thata relatively short wire link can be used (generally less than onemeter), which means not deteriorating the detector's signal-to-noiseratio.

The activation device also enables the remote control of certainfunctions that the dentist may have to use immediately before or aftertaking the image, with the same hygiene constraints. Among thesefunctions, mentioned non-exhaustively, are turning the image formaxillary/mandibular orientation, or adjusting display settings such ascontrast and brightness.

This aspect of the invention is particularly simple to implement.

It may be noted that the case has an overall elongated shape whichallows it to be easily handled and cleaned.

According to one characteristic, the encapsulated electronic module hasweight and dimensions suited to enable, when the apparatus is used, thesensor to be held in a patient's mouth when said encapsulated electronicmodule is suspended from said sensor.

According to one characteristic, the electronic module is at a distancebetween 50 cm and 2 m from the sensor.

According to one characteristic, the encapsulated electronic module isnearer the sensor than the processing and display unit.

According to one characteristic, said at least one activation device isa pushbutton.

According to one characteristic, each wire link is a cable.

According to one characteristic, as each cable is inserted at one of itsends into the case, the electronic module is fitted with anti-pulldevices that are each capable of working with one end of one of thecables to prevent the removal of the corresponding cable from the caseby a pulling action exerted on said cable.

These anti-pull devices prevent the use of electrical connectors thatcan cause false contacts and risk disconnecting unexpectedly.

According to one characteristic, as each cable has a coaxial sheath witha bundle of electrical wires, opposite the end of each cable thatinserts into the case, the part of the corresponding wire bundle is heldsolid with a metal anti-pull body of the corresponding anti-pull device.

According to one characteristic, the electronic module comes in the formof a printed circuit with overall elongated shape along a longitudinalaxis and having, at each of the two opposite ends arrangedlongitudinally, an axial cut-out open to the outside of the circuit tohouse in the longitudinal direction a metal anti-pull body and the partof the corresponding wire bundle made solid and aligned, the cut-outbeing arranged to prevent removal of the body in this longitudinaldirection.

According to one characteristic, each metal anti-pull body is providedwith fitting elements arranged on the opposite sides parallel to thedirection of the part of the wire bundle made solid with the body andwhich work together with the complementary fitting elements respectivelyarranged on the opposite longitudinal edges of the correspondingcut-out.

According to one characteristic, each part of each of the wire bundlesmade solid with an anti-pull body is held solid with a cylindrical drumthat, on the one hand, surrounds the anti-pull body and, on the otherhand, is solid with the corresponding body.

According to one characteristic, each part of each of the wire bundlesmade solid with an anti-pull body is welded directly or indirectly tothe latter.

According to one characteristic, two metal half-shells are arranged oneither side of the printed circuit board and assembled together tosecure said printed circuit board.

These half-shells protect the electronic module mechanically.

According to one characteristic, the case has at least two plastic partsforming a cover and which are assembled together to encapsulate theelectronic module.

According to one characteristic, the case has an external surface thatcan be disinfected.

According to one characteristic, the shapes of the external surface aredesigned to prevent the incrustation of dirt.

According to one characteristic, the external surface is drip-proof.

According to one characteristic, the wire link between the electronicmodule and the processing and display unit complies with standard USB2.0or can also enable transmission speeds greater than those of theabove-mentioned standard.

According to one characteristic, the sensor has an x-ray converter thatis capable of converting the x-rays that have passed through a toothinto visible light.

According to one characteristic, the biCMOS detector including theactive pixel array is capable of converting at least one part of thevisible light coming from the conversion of the x-rays into at least oneanalog electrical output signal.

According to a second aspect, the invention relates to a dentalradiology apparatus, characterized in that it comprises an intraoralsensor intended to receive x-rays that have passed through at least onetooth, said sensor including: an x-ray to visible light converter, adetector comprising an active pixel array produced using biCMOStechnology on a substrate made of semi-conductor material, and asequencer capable of generating several control signals to control theactive pixel array, said sequencer being integrated on the samesubstrate as the array.

By integrating the sequencer on the same silicon chip as the array andnot in offset electronic equipment, a reduced number of electricalsignals are required to operate the sequencer and the array and thathave to be received from outside the sensor, which is particularlyadvantageous because there are thus fewer external signals to beproduced.

This therefore enables the risks of pollution of these signals duringtheir transmission to be reduced, which contributes to not deterioratingthe detector's signal-to-noise ratio.

Furthermore, integration of the sequencer on the same silicon chip asthe array enables a detector of minimum size and simplified electronicinterface to be produced, which would not be the case if the sequencerwere a separate component.

According to one characteristic, the sequencer is capable of receivingat least one signal external to the sensor, which the generated controlsignals are based on.

Thus, for example, the sequencer is capable of receiving a single clocksignal which most of the array's internal signals derive from.

According to one characteristic, the apparatus has an electronic moduleseparate from the sensor and which is capable of generating said atleast one signal external to the sensor, which the generated controlsignals are based on.

According to one characteristic, the apparatus has a link between theelectronic module and the sensor for the transmission of said at leastone external signal.

Advantageously, the number of signals transmitted from the module to thesensor remains reasonable because of the sequencer's organization.

According to one characteristic, the link is a wire link.

According to a third aspect, the invention relates to a signalprocessing method in a dental radiology apparatus comprising anintraoral sensor that includes an active pixel array produced usingbiCMOS technology, characterized in that the method has the followingsteps: sampling of the data values held by the pixels of the arrayhaving been exposed to x-rays, generation of at least one sensor analogoutput signal based on the data values sampled on the pixels, conversionof said at least one sensor analog output signal into one digital outputsignal, and application of a correction to the analog output signal orto one of the analog output signals, to compensate in the digital outputsignal for any drifts due to the variations of the dark current in thearray.

In conjunction with this, the invention also targets a dental radiologyapparatus, characterized in that it comprises an intraoral sensorincluding: a detector comprising an active pixel array produced usingbiCMOS technology and converting x-rays received by the array into atleast one analog output signal, the apparatus comprising ananalog-digital converter for converting said at least one analog outputsignal into one digital output signal, a signal corrector that isdesigned to apply a correction to the analog output signal or to one ofthe analog output signals, to compensate in the digital output signalfor any drifts due to the variations of the dark current in the array.

According to this aspect of the invention, a correction is made to theanalog output signal delivered by the sensor so that, in the digitaloutput signal obtained following conversion of the corrected analogsignal, any drifts due to the variations of the dark current in thearray are compensated for.

As the dark current increases especially by heating during the array'soperating time, this enables an optimum adjustment of the analog chainto be conserved over time.

This aspect of the invention prevents having to over accelerate thereading of the array, which could lead to the generation of readingnoise that deteriorates the detector's signal-to-noise ratio.

According to one characteristic, the application step of a correctiontakes account of at least one value of a correction signal that isgenerated from the data values sampled on the array's pixels when it isnot exposed to any radiation.

According to one characteristic, the correction signal is generatedbetween two array exposure phases to radiation.

According to one characteristic, the correction signal is generatedregularly over time, or even irregularly.

According to one characteristic, the method comprises steps ofgeneration and analog-digital conversion of a correction and sensoroutput analog signal prior to the step of correction application.

According to one characteristic, the method comprises a step ofdigital-analog conversion of at least one value of the digitalcorrection signal into an analog correction signal that is applied tothe analog output signal or to one of the analog output signals.

According to one characteristic, the method comprises a step ofproducing a single analog output signal based on two symmetrical analogoutput signals.

According to one characteristic, the method comprises a step ofproducing a single analog output signal based on two analog outputsignals, following the step of correction application to one of the twosignals.

According to one characteristic, the step of producing a single analogoutput signal based on two analog output signals is a summing step ofthe two analog output signals.

It may be noted that producing a single signal is, for example,performed in an analog-digital converter.

According to one characteristic, the step of correction application tothe analog output signal or to one of the analog output signals isadjusted according to the law of variation in relation to the time ofthe dark current of the CMOS active pixel array and the duration ofusing this array.

According to one characteristic, the method comprises a step oftransmission of said at least one analog output signal to a electronicmodule remote from the sensor, the conversion and correction applicationsteps being performed in said remote module.

According to one characteristic, reading the array's pixels ispreferably carried out at an adjusted speed that enables the array to beread sufficiently fast to avoid deteriorating the detector'ssignal-to-noise ratio, but not so fast as to introduce any readingnoise.

According to one characteristic, the method comprises a transmissionstep of the compensated digital output signal from the remote electronicmodule to a remote signal processing and display unit.

According to one characteristic, the transmission is carried out using awire link enabling a transmission speed at least equal to that ofstandard USB2.0.

According to one characteristic, the method comprises a prior step ofreception by the sensor of x-rays having passed through at least onetooth.

According to one characteristic, the method comprises a later step ofconversion into visible light of the received x-rays, the array's pixelsbeing exposed to visible light.

According to a fourth aspect, the invention relates to a dentalradiology apparatus, characterized in that it comprises an intraoralsensor intended to receive x-rays that have passed through at least onetooth, said sensor comprising: an x-ray to visible light converter, adetector comprising an active pixel array produced using biCMOStechnology and converting the visible light thus converted into at leastone analog electrical signal, a generator of a sampling signalsynchronized with said at least one analog electrical signal and whichis intended for the later conversion of said at least one analogelectrical signal into a digital signal.

In conjunction with this, the invention also targets a signal processingmethod in a dental radiology apparatus comprising an intraoral sensorintended to receive x-rays that have passed through at least one tooth,characterized in that it includes the following steps performed in thesensor: reception of x-rays having passed through at least one tooth,conversion of the received x-rays into visible light, conversion of thevisible light thus converted into at least one analog electrical signalby an active pixel array produced using biCMOS technology, generation ofa sampling signal synchronized with said at least one analog electricalsignal and which is intended for the later conversion of said at leastone analog electrical signal into a digital signal.

According to this aspect of the invention, the fact of generating asampling signal synchronized with the analog signal supplied by thedetector will enable the sampling signal synchronized with thedetector's analog signal to be transmitted simultaneously for thepurposes of the later analog-digital conversion of said analog signal.

By transmitting these two signals simultaneously, any disturbance and/orphase difference affecting one of the signals during the transmissionwill inevitably affect the other signal and will thus be compensatable.

Further, this aspect of the invention is advantageous because it issimpler to implement than a technique according to which the clockrequired for sampling the analog signal for its conversion is producedlocally at the offset converter. Indeed, the clock has to be produced inadvance and take account of the various delays that affect the analogsignal during its transmission, which can be problematic if these delaysvary over time.

According to this aspect of the invention, on the contrary, whatever thedelays and whatever their variation over time, they are by definitioncompensatable as they affect both signals.

The signal processing according to the invention is thus more reliablethan in the prior art.

According to one characteristic, the apparatus comprises: an electronicmodule remote from the sensor, a link between the electronic module andthe sensor for the simultaneous and in phase transmission of said atleast one electrical signal and of the sampling signal.

According to one characteristic, the electronic module comprises ananalog-digital converter for converting said at least one analogelectrical signal into one digital signal based on the sampling signal.

According to one characteristic, the link between the electronic moduleand the sensor is a wire link.

According to one characteristic, the apparatus comprises a signalgenerator which is capable of generating, based on one analog electricalsignal from the detector, two differential analog electrical signals.

The transmission of these two differential signals enables latercompensation for disturbances arising on the link and that affect bothsignals.

According to one characteristic, the signal generator is integrated intothe sensor, the link ensuring the simultaneous and in phase transmissionof the two differential analog electrical signals and the samplingsignal.

According to one characteristic, the sensor comprises a sequencer thatis capable of generating several active pixel array control signals andwhich includes the sampling signal generator.

According to one characteristic, reading the array's pixels ispreferably carried out at an adjusted speed that enables the array to beread sufficiently fast to avoid deteriorating the detector'ssignal-to-noise ratio, but not so fast as to introduce any readingnoise.

According to a fifth aspect, the invention relates to a signalprocessing method in a dental radiology apparatus comprising anintraoral sensor that includes a detector including an active pixelarray produced using biCMOS technology, the pixels being arranged inrows and columns, characterized in that it comprises the followingsteps: selection of each row of the array, for each row selected,sampling of the data values held by each pixel having been exposed toradiation, generation of a read signal from the sampled data values forthe array's pixels, application at the detector's input of an inputreference signal (black-in), production of an output signal from thearray's read signal and an output reference signal (black ref)representative of the detector's intrinsic electronic drifts and whichis obtained at the detector output based on the input reference signalapplied at said detector's input.

In conjunction with this, the invention also targets a dental radiologyapparatus comprising an intraoral sensor that includes a detectorincluding an active pixel array produced using biCMOS technology, thepixels being arranged in rows and columns, characterized in that itcomprises: means for selecting each row of the array, means for samplingthe data values held by each pixel having been exposed to radiation, foreach row selected, means for generating a read signal based on thesampled data values for the array's pixels, means for applying at thedetector's input an input reference signal, means for producing anoutput signal from the array's read signal and an output referencesignal (black ref) representative of the detector's intrinsic electronicdrifts and which is obtained at the detector output based on the inputreference signal applied at said detector's input.

According to this aspect of the invention, the use of a reference signalrepresentative of the detector's intrinsic electronic drifts enablescompensation in the detector's output signal for the drifts specific tothe detector's manufacture (dispersions during manufacture) but whichvary from one detector to another.

In this way, the signal-to-noise ratio supplied by the detector isimproved compared with the techniques provided for in the prior art.

According to one characteristic, the output signal is produced byforming a difference between the array's read signal and the outputreference signal (black ref), which enables the above-mentioned driftsto be dealt with.

According to one characteristic, for each array row selected, after thefirst sampling step, the method includes a second sampling step of thedata values obtained after resetting each pixel.

According to one characteristic, the method includes a step of applyinga resetting signal to each selected row between the two sampling steps.

According to one characteristic, the array read signal is generated byforming the difference between the data values held by the array'spixels and obtained respectively after each sampling of the same pixel.

According to one characteristic, the input reference signal is DCvoltage.

According to one characteristic, the method includes a step of receivingthe input reference signal that comes from an electronic module remotefrom the sensor.

According to one characteristic, prior to the first sampling step, thepixel array is exposed to visible light coming from the conversion ofx-rays that have passed through a tooth.

According to one characteristic, the output signal that is produced isan analog output signal.

According to one characteristic, the analog output signal is deliveredby the sensor.

According to one characteristic, the method includes a step ofconverting the analog output signal into a digital output signal.

According to one characteristic, the method includes a step oftransmitting the output signal to an electronic module remote from thesensor.

According to one characteristic, the conversion step is performed in theelectronic module.

According to one characteristic, reading the array's pixels ispreferably carried out at an adjusted speed that enables the array to beread sufficiently fast to avoid deteriorating the detector'ssignal-to-noise ratio, but not so fast as to introduce any readingnoise.

According to a sixth aspect, the invention relates to a signalprocessing method in a dental radiology apparatus comprising anintraoral sensor that includes an active pixel array produced usingbiCMOS technology, the pixels being arranged in rows and columns, thesensor delivering an analog output signal produced from the data valuesheld by the array's pixels exposed to radiation, characterized in that,the pixels of at least one array column being optically inactive, themethod includes the following steps: conversion of the analog outputsignal into a digital output signal, reading in the digital outputsignal of one or more data values coming from each optically inactivepixel of an array row, reading in the digital output signal of one ormore data values coming from each optically inactive pixel of at leastone adjacent row, the relevant pixel(s) of each of the two rows beingequal in number and arranged in the same column(s), comparison of thedata value(s) read respectively for the inactive pixel(s) of a row withthe data value(s) read respectively for the inactive pixel(s) of said atleast one adjacent row, according to the result of the comparison,decision-making as to any modification in the output signal of the datavalues of all the pixels of one of the rows used for the comparison.

In conjunction with this, the invention also targets a dental radiologyapparatus comprising an intraoral sensor that includes an active pixelarray produced using biCMOS technology, the pixels being arranged inrows and columns, the sensor delivering an analog output signal producedfrom the data values held by the array's pixels exposed to radiation,characterized in that the pixels of at least one array column beingoptically inactive, the apparatus includes: means for converting theanalog output signal into a digital output signal, means for reading, inthe digital output signal, one or more data values coming from eachoptically inactive pixel of an array row, means for reading, in thedigital output signal, one or more data values coming from eachoptically inactive pixel of at least one adjacent row, the relevantpixel(s) of each of the two rows being equal in number and arranged inthe same column(s), a comparator supplying a comparison of the datavalue(s) read respectively for the inactive pixel(s) of a row with thedata value(s) read respectively for the inactive pixel(s) of said atleast one adjacent row, decision-making means capable of providing adecision as to any modification in the output signal of the data valuesof all the pixels of one of the rows used for the comparison.

According to this aspect, the sensor's digital output signal isprocessed by correcting, if necessary, the data values from the pixelsof one or more array rows to prevent the introduction of additionaldrifts in the signal, which would risk deteriorating the latter'ssignal-to-noise ratio in a way that is particularly visible on theimage.

Indeed, the deterioration would be shown by horizontal streaking of theimage due to an average noise value varying from one row to another.

According to one characteristic, when the data values compared with oneanother are different from one row to another, the method includes amodification step, in the output signal, of the data value of each pixelof the array's adjacent row.

This enables readjustment of the average level of the pixels of thecorresponding row.

According to one characteristic, the array rows are compared two by two.

According to one characteristic, when two consecutive array rows arecompared, the modification is applied to the data values of the pixelsof the second row.

According to one characteristic, the method includes the followingsteps: reading of the data values S_(i)(n), i=1 to m, comingrespectively from a number m of optically inactive pixels of a firstarray row, reading of the data values S_(i)(n+1) coming respectivelyfrom m optically inactive pixels of a second row which is the next rowof the array, determining for each of the first and second rows anaverage data value S(n), S(n+1) being obtained from the respective datavalues S_(i)(n), S_(i)(n+1) of each row, comparing the average datavalues S(n), and S(n+1) one with another, according to the result of thecomparison, decision-making as to any modification, in the outputsignal, of the data values of all the pixels of the second row.

According to one characteristic, when the compared average data valuesdiffer one from another, the method includes a modification step of thedata value of each pixel of the second row by assigning to each of thesedata values the difference between the average data values S(n), andS(n+1) to adjust the average data value S(n+1) of the second row to theaverage data value S(n) of the first row.

According to one characteristic, the method includes a step oftransmitting the analog output signal to an electronic module remotefrom the sensor, prior to the steps of reading the data values.

According to one characteristic, the conversion step of the analogoutput signal is performed in the electronic module.

According to one characteristic, the method includes a prior step ofreception by the sensor of x-rays having passed through at least onetooth.

According to one characteristic, the method includes a later step ofconversion into visible light of the received x-rays, the array's pixelsbeing exposed to visible light.

According to one characteristic, reading the array's pixels ispreferably carried out at an adjusted speed that enables the array to beread sufficiently fast to avoid deteriorating the detector'ssignal-to-noise ratio, but not so fast as to introduce any readingnoise.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages will appear during the followingdescription, given solely as a non-limiting example and with referenceto the appended drawings.

FIG. 1 a is a partial schematic view of a dental radiology apparatusaccording to the invention during the taking of an image of a tooth.

FIG. 1 b illustrates a conventional representation of an active pixelusing three transistors and a photodiode.

FIG. 2 is a partial schematic view of the dental radiology apparatusaccording to the invention and that completes the representation of FIG.1 a.

FIG. 3 is a general schematic view of the detector 22 represented inFIGS. 1 a and 2.

FIG. 4 is a schematic circuit illustrating the generation of thedetector's output reference signal (black ref).

FIGS. 5 and 6 illustrate the rate of the S-R signals before and afterthe double sampling that is performed in circuit 76 of FIG. 3.

FIGS. 7 a and 7 b respectively represent the rate of the input andoutput signals of circuit 79 of FIG. 3.

FIG. 7 c represents the rate of the sampling signal Sample-clk.

FIG. 7 d schematically represents the analog-digital conversion of thevideo signal using the sampling signal.

FIGS. 7 e to 7 g successively and schematically illustrate thecorrection applied to the analog signal V- to compensate for thevariations of the dark current.

FIG. 7 h shows the advantage of the dark current compensation on thegray levels obtained in the video signal.

FIG. 8 is an algorithm of a computer program executed in the centralprocessing unit 44 of FIG. 2.

FIG. 9 is a general schematic view of the removable part of the dentalradiology apparatus according to the invention and that is representedas deployed.

FIG. 10 is a situational view of the dental radiology apparatusaccording to the invention during the taking of an image of a tooth.

FIG. 11 is an exploded view of the electronic module 32, its anti-pulldevices and metal protector half-shells.

FIG. 12 is an exploded perspective view showing the installation of ametal anti-pull body and the related cable in the electronic module 32.

FIG. 13 is a partial schematic view of one of the ends of the electronicmodule equipped with an anti-pull body and a related cable.

FIG. 14 is an exploded perspective view of the various elements housedinside the case 180.

FIG. 15 is a partial schematic view of one of the end sleevesrepresented in FIG. 14.

FIG. 16 is a schematic perspective view of the various parts of FIG. 14once assembled.

DETAILED DESCRIPTION OF THE INVENTION

This is a Continuation of U.S. Ser. No. 13/188,497 titled DENTALRADIOLOGY APPARATUS AND SIGNAL PROCESSING METHOD USED THEREWITH filed onJul. 22, 2011 in the names of Boucly et al, which was a Continuation ofU.S. Ser. No. 12/505,556 titled DENTAL RADIOLOGY APPARATUS AND SIGNALPROCESSING METHOD USED THEREWITH filed on Jul. 20, 2009 in the names ofBoucly et al, which issued as U.S. Pat. No. 8,008,628, which was aDivisional application of U.S. Ser. No. 10/580,395 titled DENTALRADIOLOGY APPARATUS AND SIGNAL PROCESSING METHOD USED THEREWITH filed onApr. 27, 2007 in the names of Boucly et al, which issued as U.S. Pat.No. 7,608,834, which claims priority to PCT/EP2004/012885 filed on Nov.13, 2004, which claims priority to EP 03292901.0 filed Nov. 21, 2003.

As represented in FIG. 1 a, an x-ray dental radiology apparatus 10comprises an x-ray source 12 placed outside a patient's mouth and anintraoral radiation sensor 14 placed in a patient's mouth, behind atooth 16, and which is capable of receiving the x-rays that have passedthrough the tooth.

The sensor 14 comprises, in the propagation order of the radiation, ascintillator 18 that converts the x-rays that have passed through thetooth into visible light, a fiber optic plate 20 that, on the one hand,includes metal particles intended to absorb the part of the x-raysreceived by the scintillator and not converted into visible light and,on the other hand, conducts the visible light thus converted to adetector 22. This detector is mounted on a ceramic substrate 24 andconverts the visible light from the glass fibers into one or more analogelectrical signals.

The various components of the sensor 14 are assembled together, forexample, by gluing.

The scintillator 18 is, for example, made from gadolinium oxysulfide.

Alternatively, it can be made from cesium iodide, lutetium crystals orany element having the property of converting x-rays into visible light.

The fiber optic plate 20 is, for example, marketed by SCHOTT with thecommercial reference 47 A or by HAMAMATSU with commercial reference XRS.

The biCMOS detector 22 is an APS type detector (Active Pixel Sensor)using biCMOS manufacturing technology, i.e. using both NMOS and PMOStransistors, as against passive pixel detectors. For further details onthe biCMOS detector, document EP 0 858 111, for example, may be referredto.

An active pixel integrates amplification means of the electrical chargecollected on the light sensitive pixel element.

The amplified electrical charge held by an active pixel is referred toin the rest of the description as “data value” and is representative ofthe quantity of light captured by the pixel.

The biCMOS detector 22 represented in FIG. 2 is a chip produced on asilicon substrate 28 according to the biCMOS manufacturing technologyand that includes an active pixel array 26 and a sequencer 30 integratedon the same substrate.

The pixels structure is, for example, the known structure illustrated inFIG. 1 b and utilizing three transistors T1, T2, T3 and a photodiode P.

Preferably, the photodiode has a shape suited to optimize the pixel'sfill factor, while guaranteeing sufficient channeling of the chargesgenerated at the photodiode by the impact of photons.

Indeed, the shape of the photodiode has to enable the reliableseparation of the pixels one from another to prevent the chargegenerated at one pixel from being collected by one of the adjacentpixels (crosstalk).

However, it should be noted that the shape of the photodiode is not tooccupy too great a part of the pixel's surface area to prevent the fillfactor from being decreased.

The sequencer 30 is capable of generating several control signals tocontrol the array.

To do this, the sequencer receives one or more signals external to thesensor and from which the various array control signals are generated.

The radiology apparatus 10 comprises an electronic module 32 remote fromthe sensor 14 and thus the detector 22 of FIG. 2 and which is linked tothis sensor by a wire link 34 that is a cable.

For example, the cable is of the multi-wire or multi-strand type, thehigh-frequency signals (clock, video, etc.) can optionally be channeledby coaxial cables with the assembly being shielded by a ground braid.

The above-mentioned external signal(s) is(are) generated in theelectronic module 32 and transmitted using the cable 34 to the detector22 and, more particularly to the latter's sequencer 30.

One of the external signals is, for example, a unique clock signalClk-x, for example having a frequency of 12 MHz and from which manyinternal signals required for the operation of the array 26 will begenerated by the sequencer.

It is especially advantageous to arrange the sequencer in the detector22 and not in the electronic module 32, because the single transmissionof a restricted number of signals including the unique clock signalcoming from the module 32 is enough.

Indeed, if the sequencer were arranged in the electronic module 32, itwould then be necessary to transmit by the cable 34 very many signalsintended to control the array, which would cause additional noise,especially because of the crosstalk created between the various signalstransmitted in the cable.

In this way, arranging the sequencer in the detector 22, and especiallyon the same substrate as the array, enables the detector'ssignal-to-noise ratio to be improved.

In the same way, the number of wires running in the cable is alsoreduced, which enables the use of a more flexible cable than if thelatter has to carry the many control signals required to operate thearray.

This is also advantageous insofar as the cable 34 leaves the patient'smouth when the sensor is placed inside, behind a tooth, and it istherefore necessary to have a cable as flexible as possible to minimizethe inconvenience caused to the patient.

It may be noted that the integration of the sequencer on the samesubstrate as that of the array enables the detector's overall dimensionsto be reduced, and thus the sensor's, which is a prime requirement foran intraoral sensor.

Indeed, a sequencer produced as a quite separate component apart fromthe detector's chip would inevitably lead to a more bulky sensor andthus to more inconvenience for the patient.

The reduction of the number of signals to be generated by the sequencertends to make it less bulky.

It may be noted that the electronic module 32 is placed at a distancefrom the sensor of at least 50 cm so as to not inconvenience the patientor even the dentist and at a maximum distance of about 2 m from thesensor for reasons that are to be developed later.

As will also be seen below, one or more analog output signals areproduced in the sensor and transmitted by means of the cable 34 to theelectronic module 32 wherein they undergo several processes.

In particular, the module 32 includes two amplification units 36 and 38which each amplify one of the analog output signals that it receives ininput and a filtering unit 40 of the two previously mentioned signals.

Optionally the unit 40 can be designed to produce a single analog outputsignal based on the two output signals, in addition to the filteringfunction.

The filtered analog output signals are then joined into a single analogsignal that is converted into a digital signal in an analog-digitalconverter 42 and transmitted to a central processing unit 44.

The central processing unit 44 includes more particularly a clock 48, amicroprocessor 50 and a memory 52.

This processing unit 44 performs, among other things but notexclusively, operations of putting the detector into operating mode, asopposed to the standby periods; points the digitized signal to theoutput interface 60 described below; manages a memory 52 intended, forexample, to contain the list of defective elements of the array 26 ofthe detector 22 or the detector's serial number; looks in the digitizedvideo signal for data characteristic of the presence or not of x-rays;and manages the activation device 100 described later.

It may also be noted that a correction applied to one of the analogsignals amplified by the unit 38 by means of a digital correction signalthat comes from the central processing unit 44, is converted into ananalog correction signal by a digital-analog converter 46 and is thenapplied to the unit 38.

The unit 38 performs the function of a subtractor amplifier.

The radiology apparatus 10 also includes a processing and display unit54 remote from the electronic module 32 and linked to the latter bymeans of a wire link 56 which is, for example, a cable.

The processing and display unit 54 is, for example, a computer thatreceives the output signals of the sensor 14, once digitized andprocessed in the electronic module 32, in order to carry out on thelatter appropriate image processing that is known to those skilled inthe art to be able to view on the display screen 58 the image of thetooth 16 of FIG. 1.

An interface 60 in compliance with standard USB2.0 is provided at theoutput of unit 44, and a serial bus USB2.0 and an correspondinginterface in the remote computer 46 (not shown), so that the signalsdelivered by the module 32 are transmitted to the remote computer 54 athigh speed, for example about 480 Mbps.

The use of such an interface thus enables the high speed transmission tothe computer of data that are supplied by the CMOS 22 detector andprocessed by the module 32.

The use of this interface is particularly well suited to the use of ahigh frequency clock signal, for example 12 MHz, for sampling the datacollected by the array of the biCMOS detector 22, that is without havingto use a buffer memory to store the data before their transmission tothe computer.

Indeed, this clock signal frequency represents a good compromisebetween, on the one hand, too low a frequency to sample the array, whichwould cause an increase of the dark current between the start and end ofthe array sampling and, on the other hand, too high a frequency whichwould generate additional reading noise and disturb the detector'soutput signal.

Indeed, given the constraints linked to dark current development in thedetector over time, the array's pixels have to be sampled at arelatively high frequency, which can be incompatible with thetransmission speed permitted by standard USB1.

It should be noted that the USB2 bus of the cable 56 carries digitizedimage signals that are to be transmitted to the unit 54 and a singlevoltage signal 61 that will act to operate the CMOS detector followingcleaning in a circuit 62 of the electronic module 32.

Indeed the biCMOS detector operates using a single power supply voltage,for example, 5 volts and TTL control levels, unlike a charge-coupleddetector (CCD) for which four or five different voltage levels have tobe generated and many clocks.

It should be noted that the generation of the various voltage levelscauses the appearance of additional noise that disturbs the sensor'scorrect operation and that this phenomenon is thus avoided in theapparatus according to the invention.

The circuit 62 is to some extent a DC-DC converter which cleans thepower voltage supplied by the USB2 bus and which also deals with thevariations of the 5 volts of this bus by stabilizing it.

It may also be noted that the DC voltages generated by the converter 62can be continuous, for example for use by the central processing unit44, or switched, for example for use by the detector 22, which is onlypowered during use periods in the mouth. This switching is performed bythe central processing unit 44.

It may be noted that the data transmission speed on the wire link 56 hasto be at least equal to that provided by standard USB2.0 in order to beable to empty the array 26 rapidly without having to make use of abuffer memory.

FIG. 3 represents in a more detailed way the arrangement of the activepixel array 26 and the sequencer 30 on the common substrate 28 of thedetector's chip.

The array 26 is linked to a circuit 70 for selection piloting andresetting the rows L₁, L₂, L₃ . . . L_(n) . . . , L_(N) of the array.

A circuit 72 of shift registers controlled by the clock andsynchronization signals enables the circuit 70 to be controlled for thesuccessive operations of row selection and resetting.

The array is also connected to an amplification circuit 74 of columnsC₁, C₂, C₃ . . . , C_(n) . . . , C_(I) of the array and whichmultiplexes on an output amplification circuit 76 the image datacaptured by said array.

A circuit 78 of array column shift registers is provided to control theoperation of the circuit 74 and, especially, to pilot the reading of thepixels of each array row.

As stated above, the detector receives several signals from theelectronic module 32 and, especially, the signals Clk-x, Clk-y andSync-y from which all the array's internal signals are derived.

The signal Clk-x is a clock signal, for example, at 12 MHz which acts topilot the column shift registers and constitutes the principal clocksignal from which the sequencer 30 generates all the signals, andespecially the array control signals.

The control signal Sync-y acts to initialize the reading of the array.

The signal Clk-y is the control signal of the row shift registerscontrolling the circuit 72.

The reading of the image data captured by the array is performed asfollows.

The signal Sync-y, applied at the same time as the signal Clk-y,initializes the shift registers of the array's rows and causes theselection of the first row of the array.

A first selection signal of the first row of the array, which isgenerated by the sequencer 30, is tripped, for example, on a risingfront of the clock signal Clk-y, and controls the selection of the firstrow of the array.

The application of the signal Clk-x will cause the appearance of thevideo signal (output signal) at the detector's output.

The application of only the signal Clk-y will cause the selection of thenext row of the array.

This continues until all the rows have been read, and then thecombination of the signals Sync-y and Clk-y is applied again to selectthe first row of the array again.

For the selected row thus considered, the various data values held byeach of the row's pixels having been exposed to radiation will undergo afirst sampling step, also called reading step, at a rate set by theclock signal Clk-x.

Each value of the pixel's light data is stored in the columnamplification circuit 74.

Following a first sampling step of the first row's pixels, a Resetsignal is generated by the sequencer in order to reset all the pixels ofthe relevant row.

This resetting step initializes all the pixels of the selected row to areference data value specific to each pixel.

This is a data value corresponding to an unlit pixel, also called darkdata value.

After initialization of the pixels of the relevant row, a secondsampling or reading step of the reference data values held by each pixelis performed, at the rate set by the clock signal Clk-x that selects thevarious columns of the array.

The sampled reference data values are stored in the column amplificationcircuit 74 where they are added to the light data values already storedand coming from the first sampling step.

The two types of data values are then multiplexed on two busesrespectively, one carrying a read signal S (light data values) and theother carrying a re-initialization signal R (reference data values).

The data coming from these two buses are multiplexed on the outputamplification circuit 76 according to a rate set by the clock signalClk-x which activates the column shift registers.

An S-R output signal is created by the output amplification circuit 76based on the difference between the read signal S and there-initialization signal R and a reference signal that is representativeof the electronic drifts intrinsic to the detector.

This reference signal comes from an input reference signal “black-in”,which is a DC voltage coming from the module 32 and applied at thedetector input. The reference signal “black-ref” is created as shown inFIG. 4.

The circuit of FIG. 4 is representative of the way noise is generated inthe detector and the black-in signal applied at this circuit's inputundergoes drifts as it goes through the array.

Therefore, this circuit comprises a transistor 71 that acts as buffermemory for the black-in input signal and is also shown schematically inFIG. 3.

A resistor 73 and capacitance 75, whose values are appropriatelyselected according to the detector, are representative of the detector'sintrinsic elements.

An amplifier 77 amplifies the signal obtained after it has undergone thedistortions caused by the elements 71, 73 and 75 and the black-refamplified signal is thus delivered at the detector's output 22.

The signal obtained before going into the amplifier 77 (“non-amplifiedreference signal”) is supplied to the output amplification circuit 76where, with the clock signal Clk-x, on one of the rising or fallingfronts of the signal Clk-x the strongest value of the S-R signal isselected and, on the other front, the value supplied by thenon-amplified reference signal is selected, as illustrated in FIG. 5.

Thus an S-R signal is obtained whose highest values are those of thearray read signal and whose lowest values are those of the non-amplifiedreference signal, these latter values varying over time.

The S-R signal obtained (FIG. 6) is representative of the tooth's imagedata captured by the detector's pixels.

FIG. 7 a represents the overall rate of the R-S signal of the detector'soutput (FIG. 3) and the black-ref output reference signal.

As shown in FIG. 3, the analog electrical signal of the detector's S-Routput is converted by a signal generator 79 into two differentialanalog electrical signals V+ and V−.

The generator 79 is a two-output amplifier which subtracts the black-refsignal from the S-R signal and delivers differential signals V+ and V−whose rate is shown in FIG. 7 b.

The superimposition of the difference between the S-R signals and theblack-ref output reference signal avoids any drifts due to thedetector's construction that are constant over time and that vary fromone sensor to another.

By transmitting the image signal from the sensor in differential form,the various disturbances it may be subject to are avoided.

Indeed, as each of the two signals V+ and V− is subject to the samedisturbances, by reconstituting a single signal the disturbances foundon each of the signals V+ and V− can thus be avoided, which would not bethe case if only the image signal were transmitted.

Furthermore, the transmission of a differential image signal alsoindirectly enables the sensor's signal-to-noise ratio to be improved.

A sampling signal Sample-clk is generated by the sequencer (FIG. 3) and,by construction, is perfectly synchronous with the S-R output signalinsofar as the sequencer knows exactly when the data will arrive at thedetector's output. The sampling signal is produced by a phase differencesuited to the clock signal Clk-x and is shown in FIG. 7 c.

This sampling signal which is in phase with the S-R output signal, andthus with the differential signals V+ and V−, will be transmittedsimultaneously with the latter by the cable 34 intended for theelectronic module 32.

The simultaneous transmission of in-phase signals will enable, insidethe electronic module 32, conversion of the differential analog signalsto be performed in the analog-digital conversion circuit 42 at thefrequency set by the sampling signal.

By transmitting the signals simultaneously, this enables phase errorsarising in the cable to be avoided insofar as a phase error affectingboth the differential analog signals and the sampling signal can becompensated for.

In the same way any other disturbances affecting the signals duringtheir transmission are avoided.

As shown in FIG. 2, the differential analog output signals V+ and V− arerespectively amplified in the amplification circuits 36 and 38 beforebeing transmitted to the filtering circuit 40.

The signals thus filtered are transmitted to the analog-digitalconverter 42 where they are summed to produce a single signal and thissignal is digitized using the sampling signal Sample-clk (for example onthe rising front of the sampling signal, as shown in FIG. 7 d) beforereaching the central processing unit 44.

In order to avoid time variation of the dark current, which is definedas being the electric current collected at the detector output when thelatter is not exposed to any radiation, a correction signal is generatedbetween two phases of exposure to radiation of the array that are, forexample, successive.

It may be noted that the generation of such a signal can be regular ornot over time.

Thus aside from the sensor taking a tooth image, a sampling of the datavalues held by the pixels of the array when this is not exposed to anyradiation is carried out. The array reading signal that is generated isa correction signal.

Similarly to the above description for the output signals V+ and V−, thereading signal, in the absence of radiation, is transmitted indifferential form in the cable 34 and then amplified in theamplification circuits 36 and 38 before being reconstituted as a singlesignal by the circuit 40 and digitized in the converter 42.

This digitized signal is introduced into the central unit 44 in whichthe microprocessor calculates an average value of this digitized signalwhich is not zero, unlike what should be obtained in the absence ofradiation. This average value is injected into the analog digitalconverter 46 to convert it into an analog correction signal applied toone, 38, of the amplification circuits that is a subtractor circuit.

The application of this correction signal to one of the output analogsignals, here the signal V−, enables this signal's amplitude to beoffset by adjusting this signal towards the top as shown in FIGS. 7 eand 7 f.

FIG. 7 e shows very schematically the rate of the differential outputsignals V+ and V− which are each offset in relation to the zero level bythe same value.

By measuring an average value (2× offset) on the digitized correctionsignal and by applying it, after analog digital conversion, to theanalog output signal V−, the latter is offset by a corrected value of 2×offset, as shown in FIG. 7 f, to adjust it to the bottom level of theother non-corrected analog output signal V+.

When the signal V+ and the corrected signal V− are filtered andcombined, then the compensated analog signal shown in FIG. 7 g isobtained that goes from zero up to a maximum amplitude of2×(max-offset), where the “max” value designates the maximum amplitudein absolute value of each of the signals V+ and V−.

The compensated analog signal is then digitized in the circuit 42.

Thus variations due to the dark current in the array are avoided.

FIG. 7 h, which shows the number of pixels according to the gray levelspresents in the video signal, illustrates this compensation phenomenonby demonstrating the rate of the histogram of the video signal beforeand after the application of a correction.

It may be noted that it is preferable to convert the correction analogsignal rather than applying it directly to one of the output analogsignals, as soon as the electronic module 32 receives the correctionsignal.

Indeed, this would require storing the correction analog signal with allthe risks of drifts and/or volatility that this involves.

By performing this correction digitally, these problems are avoided andin addition the analog-digital converter is integrated into thecompensation, which avoids affecting the digitizing process with a driftspecific to the converter.

Further, it may be noted that a correction analog signal can also beapplied to the other output analog signal V+, or even to the two signalsV+ and V−.

The application of a correction to the two signals makes the processsymmetrical.

The application of a correction to one of the analog output signals orto the single analog signal is adjusted according to the law ofvariation according to the time of the dark current of the array and theduration of use of this array.

Indeed, knowing these two settings, it is possible to plan at whatmoment the dark current is liable to vary most and thus to envisageperforming a correction to compensate for the drifts due to thesevariations.

As explained above, at the time of reading the array and, moreparticularly, after having carried out a first sampling of the pixels ofa selected row of the array, a reset signal is applied to the relevantarray row by means of the circuits 70 and 72 (FIG. 3) to reinitializethe row's pixel values to the reference data values (dark data values).

However, if the reset signal varies from one row to another, an error isintroduced into the data values held by the row's pixels, which resultsin offsets in relation to zero: the data value held by a pixel after itsre-initialization is not zero as it should be in theory, but has anoffset in relation to zero and, what is more, this offset can vary fromone row to another.

The introduction of an additional error results in a deterioration ofthe signal-to-noise ratio supplied by the detector.

More especially, with such errors, a “horizontal combing” noise isintroduced into the image signal produced on the screen 58 of thecomputer 54 (FIG. 2).

To remedy this problem, a number m of pixels of each of the array rowsis first arranged to be made optically inactive, the optically inactivepixels of the various rows being equal in number (e.g. equal to 3) andarranged in the same array columns.

It may be noted that the pixels made optically inactive are arranged inthe first array columns but may well also be found somewhere else, suchas in its last columns.

It may be noted that the number m of optically inactive pixels can varyaccording to the accuracy that is required for the drift compensationintroduced with the re-initialization signal.

The number m can also vary according to the size of the array.

In the embodiment example illustrated in FIG. 3, the rows L₁, L₂ . . .L_(n) . . . L_(N) each respectively contain three “blind” pixelsP_(1.1), P_(1.2), P_(1.3), P_(2.1), P_(2.2), P_(2.3) . . . P_(n1),P_(n2), P_(n3) . . . P_(N1), P_(N2) and P_(N3).

To make a pixel optically inactive, metallization or serigraphy, forexample, is carried out on these pixels.

Then processing of the detector's output signal is performed afterdigitization by the circuit 42 (FIG. 2).

The processing is applied to the signal by the central processing unit44 by means of the processor 50 which will execute a series ofinstructions provided for in the algorithm of FIG. 8 which is stored inthe memory 52.

This algorithm includes a first initialization step S1 during which thevariable n representative of the array's rows is initialized to thevalue 1.

During the next step S2, the data values S_(i)(n) of the row n of thearray are read for the three blind pixels P_(n1), P_(n2), P_(n3).

These values are read in the digitized output signal.

During the next step S3, the data values S_(i)(n+1) are readrespectively from the three optically inactive pixels P_(n+1.1),P_(n+1.2), P_(n+1.3) of the next row n+1 of the array.

After having read the data values from the optically inactive pixels oftwo consecutive rows n and n+1 of the array, during the next steps S4and S5, for each of the rows n and n+1 an average data value S(n),S(n+1) is determined that is obtained based on the respective datavalues S_(i)(n), S_(i)(n+1) of each row.

The higher the number m, the better the accuracy in determining theaverage value.

The average data value is, for example, obtained by performingarithmetic averaging.

During the step S6, the absolute value of the difference between the twopreviously determined average values is determined.

The next step S7 is a test that makes a comparison between the averagedata values S(n) and S(n+1).

In theory, one examines whether the two average values are equal but, inpractice, one compares the result obtained in the step S6 with athreshold value E that takes into account, for example, the order ofsize of the differences that it is technically possible to detectbetween the average values.

When no significant difference is found between the average data valuesS(n) and S(n+1), then the next step S8 is a test during which one checkswhether the variable representative of the number of rows n is equal tothe total number N of rows in the array.

If yes, the algorithm is stopped.

If not, if array rows remain to be processed, then step S8 is followedby a step S9 during which the variable n is incremented by one unit andthen the steps that have just been described are performed again.

When the result of the test made in the step S7 is positive, then it isdecided to modify the data values of all the pixels of the row n+1 inthe digital output signal as illustrated by the step S10.

During this step, the data value coming from each of the pixels I of therow n+1 and which is noted S_(i)(n+1) is modified by assigning to it theabsolute value of the difference determined in step S6, in order toadjust the average data value S(n+1) of the row n+1 to the average datavalue S(n) of the row n.

The step S10 is then followed by step S8 as described above.

By continuing in this way for each pair of consecutive rows, each of thearray rows is corrected, except for the first and thus the image ishomogenized row by row in order to suppress the above-mentioned“horizontal combing” noise.

It may be noted that it is also possible to make a comparison, not ontwo consecutive rows of the array but on three consecutive rows.

In this case, each of the data values from the m optically inactivepixels of a set of three consecutive rows of the array are read and anaverage data value is determined for each of these rows.

After comparison of the average data values of the three rows, accordingto the result of the comparison, one then decides to modify or not thedata values of all the pixels of the second row in the digital outputsignal.

FIG. 9 shows the physical embodiment of a dental radiology apparatusaccording to the invention that includes the intraoral sensor 14, theelectronic module 32 integrated in a case, to be described later, thetwo parts being interlinked by a cable 34, and a connector 80 linked tothe module 32 by the cable 56.

The connector 80 is intended to work together with a complementaryconnector of the processing and display unit 54.

It may be noted that the cable 34 is relatively short insofar as itcarries the analog signals that risk being over attenuated if the cablewere too long.

This arrangement enables the constraints specific to dental radiology tobe taken into account and especially because the intensity of thesensor's output signal 14 is limited by the fact that the x-ray dosegoing through the patient's tooth is necessarily maintained as low aspossible in order not to expose the latter to too great radiation doses.

Therefore, the length l of the cable 34 is generally less than 2 meters.

The reduced length l of the cable 34 thus enables the sensor 14signal-to-noise ratio not to be deteriorated.

On the other hand, this length l is generally more than 50 cm in ordernot to cause additional discomfort by placing it too near the patient'smouth.

However, it may be noted that the length L of the cable 56 thattransmits the digital signals is not limited and can, for example, equalseveral meters and, in particular, be between 2 and 5 meters long.

The electronic module 32 includes a detector activation device 100 thatis, for example, in the form of a pushbutton.

This device 100 is especially useful for dentists to activate the sensor14 detector and put it into a state to receive and process x-rays thathave passed through the patient's tooth 16, insofar as the module 32 isplaced, when in use, within the dentist's sphere of activity.

This means that he/she can then, without having to move, hold the module32 and press the detector's activation device 100.

This arrangement saves the dentist from moving to the remote unit 54 toclick on a computer mouse with the surgical gloves that he/she used toput the sensor 14 into the patient's mouth and which are thus alreadycontaminated, especially by the patient's saliva.

It may be noted that in the prior art, by clicking on the mouse, theintraoral sensor is activated by means of a software interface.

Thus the risks of crossover contamination with another patient areprevented insofar as the mouse is not generally part of the equipmentthat is disinfected after use.

After activating the sensor using the activation device 100, the dentiststarts the x-ray generator 12 using a switch device 102 such as anelectrical pushbutton switch (FIG. 10) that he/she has within reach.

Further, as shown in the FIG. 10, at the time of using the dentalradiology apparatus according to the invention, the encapsulatedelectronic module is suspended from the sensor 14 when this is placed ina patient's mouth, which enables it to be within reach of the dentistwhen he/she is wearing gloves and has just installed the sensor in thepatient's mouth.

Indeed it is possible to suspend the electronic module encapsulated inits case at the end of the cable 34 linking it to the sensor insofar asit has been designed so that its weight and dimensions enable this use.

Indeed, too high a weight would risk pulling on the cable 34, and thusexerting a pull on the sensor 14, which would be felt by the patient andcause an additional discomfort.

Furthermore, reasonable dimensions of the encapsulated module are suitedto the size of an adult's hand and thus do not cause additionaldiscomfort linked to the size, either for the dentist, or for thepatient.

It may also be noted that the activation device 100 of the electronicmodule 32 or several activation devices can be used to execute otherfunctions.

Insofar as a single activation device 100 is used, these other functionscan be implemented by successively pressing on the latter.

Thus, when an image is being taken by the sensor or even after the imagecapture, it is useful to be able to supply data on the direction oforientation of the image to the image processing software installed inthe remote unit 54, for example, according to whether an image of a toptooth is taken, whether the sensor is placed horizontally to take animage of an occlusion, or even whether an image of a bottom tooth istaken.

Thus, by several successive presses on the device 100, one can mark inwhich position the sensor has been placed by the dentist.

For example, one press on the device 100 switches on the sensor andindicates that this is taking the image of a bottom tooth, two briefpresses switch on the sensor and indicate that this is taking the imageof an occlusion with the sensor placed horizontally, while threesuccessive presses switches on the sensor and indicates that the imageis rotated insofar as a top tooth has been taken vertically.

Other functions such as, for example, the adjustment of image brightnessor contrast, can also be controlled by activating the device 100.

As shown in FIG. 11, the electronic module 32 has the form of a printedcircuit board 150 with overall shape elongated along a longitudinal axisX.

The printed circuit board 150 here has an overall rectangular shape andhas, at each of its two opposite ends 150 a, 150 b that are arrangedlongitudinally according to the axis X, an axial cut-out 152, 154having, for example, a rectangular shape open towards the outside of thecircuit.

The axial cut-outs 152, 154 are intended to house a metal anti-pull body156, 158 (FIG. 11) according to the circuit's longitudinal axis.

The electronic module 32 is equipped with two anti-pull devices that areeach capable of working together with one of the ends of one of thecables 34 and 56, so as to prevent the removal of the correspondingcable from the electronic module and from the case by a pulling actionexerted on said cable.

Each cable has a sheath (sheath 56 a for the cable 56 in FIG. 12) thatis coaxial with a bundle of electrical wires (bundle 56 b of the cable56).

Opposite each end of each cable that is inserted into the case, as willbe seen later, the part of the corresponding wire bundle 56 b, oppositethe end 56 c of the cable 56, is held solid with the metal anti-pullbody 158.

It may be noted that everything that is described for the cable 56 andthe metal anti-pull body 158 is valid for the cable 34 and the anti-pullbody 156.

Each of the wire bundles (cable braid) is made solid with thecorresponding metal anti-pull body by means of a cylindrical drum,marked 160 for the body 156 and 162 for the body 158, which itself is anintegral part of said body.

More particularly, the cable, for example the cable 56 of FIG. 12, isstripped at its end 56 c so that the wire bundle 56 b can be introducedinside the drum 162 and, then, a weld of the end part of the wire bundlecan be made in the drum.

Thus, the wire bundles are made solid indirectly to the metal anti-pullbody by means of the corresponding drum, but one can very well envisagewelding the wire bundles directly to the body itself.

As shown in FIG. 11, the metal anti-pull bodies 156 and 158 areintroduced into the corresponding longitudinal slots or cut-outs 152 and154 perpendicularly to the longitudinal axis X of the circuit 150.

This can be explained by the fact that each metal anti-pull body isprovided with fitting parts arranged on the opposite sides parallel tothe direction of the end part of the wire bundle that is made solid withthe body (FIG. 12), a direction that is akin to the longitudinal axis Xof the circuit 150 when the metal anti-pull body is in position on saidcircuit.

More particularly, the fitting parts 158 a and 158 b of the anti-pullbody 158 have the form of projections present over the whole height ofthe body (FIG. 13) and which work together with the complementaryfitting parts arranged respectively on the opposite longitudinal edgesof the corresponding cut-out.

These complementary fitting parts have the form of transversal notchesthat are shown in FIG. 11 and, more visibly, in FIG. 12 for the cut-out152.

These notches 152 a and 152 b work together with the projecting fittingparts of the corresponding body and constitute a mortise-and-tenon typeassembly.

The notches 154 a and 154 b of the cut-out 154 by which the metalanti-pull body 58 is introduced are shown in FIG. 11.

It may be noted that the fitting parts of the anti-pull body and thecomplementary parts arranged in the corresponding cut-out constituteaxial holding parts of the anti-pull body, preventing any axial removalof the body in relation to the printed circuit board 150.

These fitting parts also facilitate the installation of the metalanti-pull body by an appropriate guiding in a transversal direction(FIG. 11).

The presence of the anti-pull devices means avoiding the use ofelectrical connectors, which is particularly advantageous.

Indeed, the use of electrical connectors would risk leading to unwanteddisconnections, which is not desirable when the patient has just beenexposed to a dose of x-rays and it is then necessary to expose him/heragain to this radiation after having re-established the electricalconnection at the electronic module.

Besides, the presence of electrical connectors equipped withsophisticated locking systems is not very desirable insofar as thiswould complicate the apparatus and add weight and volume to theelectronic module encapsulated in its case, which is especially to beavoided.

Furthermore, the presence of an electrical connector close to thepatient can become problematic for safety raisons in the case ofunwanted disconnection or faulty contact.

On the other hand, the case 180 that encloses the electronic module hasto be disinfected after each intervention of the dentist. But thepresence of a male electrical connector and a female electricalconnector requires receptacles for the connector branches and sucharrangements create places that can never be sterilized, at leastsatisfactorily.

Besides, leak tightness problems risk arising during sterilization,which is not acceptable.

Each anti-pull body is also provided, on its two parallel opposite sidesthat carry the fitting parts, with two transversal end-stop partsarranged either side of one of the fitting parts and that are referenced158 c, 158 d, for those around the fitting part 158 a, and 158 e and 158f for those around the fitting part 158 b (FIGS. 12 and 13).

These transversal end-stop parts are shorter than the fitting parts sothat, when the fitting parts of each anti-pull body are introducedinside the cut-out's corresponding openings, the transversal end-stopparts come up against the cut-out's longitudinal edges to immobilize theanti-pull body in this position (FIG. 13).

It may be noted that the fitting parts arranged, on the one hand, on themetal anti-pull body and, on the other hand, on the edges of thecorresponding cut-out can be reversed, in the sense that the body can beprovided with longitudinal grooves and the cut-out with correspondingpins.

Other fitting parts can be envisaged (dovetail joint assembly, severalnotches on each edge of the cut-out, notches of different shapes, etc.).

It may be noted that the board 150 includes an activation device 100shown in the form of a pushbutton and that enables the detector to beactivated when a tooth image has to be taken.

As shown in FIG. 11, two metal half-shells 164 and 166 are arranged oneither side of the printed circuit board 150 and assembled together, bymeans of a weld bead, to secure said printed circuit board.

These metal shells are assembled after the metal anti-pull bodies aremade solid with the cables 34 and 56, after these bodies are positionedin the corresponding cut-outs of the circuit 150 and after theelectrical connections 168 with the board (FIG. 12) are put into place.

It may be noted that the metal anti-pull bodies also act as spacers toenable the fixing of the metal half-shells.

The latter fulfill several functions:

-   -   a first function of these metal half-shells is to ensure        electrical continuity across the two cables 34 and 56;    -   a second function is thus to provide a Faraday cage for        electromagnetic compatibility purposes;    -   a third function of these half-shells is to mechanically protect        the electronic module 32.

Two end-sleeves 170 and 172 are provided to enable the routing of thecorresponding cables 56, 34 by means of a longitudinal conduit 174 (FIG.15).

These sleeves, such as the sleeve 172 of FIG. 15, include longitudinalrecesses 176, 178 which lend them some flexibility. This flexibilityprevents shearing of the cable that could occur following the repeatedhandling and distortion it undergoes.

These sleeves also ensure the leak tightness of the cable and the caseinterior.

The case 180 shown in FIG. 16 and which encapsulates the electronicmodule 32 already protected by the two metal half-shells 164 and 166 hastwo plastic parts forming a cover 182, 184 (FIG. 14).

These two parts with overall elongated and more particularly oblongshape are assembled together, for example, by gluing or US welding so asto enclose the electronic module 32.

One may note the presence on each of the end sleeves 170 and 172 of acollar 186, 188 (FIGS. 14 and 15) and an opening with at least partiallycomplementary shape made at the ends of each of the parts 182 and 184forming the cover.

In FIG. 14, the top half-cover 182 has two openings, of which one 190 isshown, and the bottom half-cover 184 has two openings 192 and 194, bothshown.

When the two half-covers are assembled on either side of the electronicmodule 32, the openings of each half-cover slot into the collar and thelatter's body to axially hold solid the case and the end-sleeves thatextend it.

The openings arranged at the ends of the top and bottom half-covers thusconstitute the holding edges of the corresponding sleeves.

One may also note the presence inside the top half-cover 184 oftransversal guide walls 196 and 198, which are recessed to enable thepositioning of the corresponding cable.

Transversal stiffening ribs 200, 202 and 204 as well as a longitudinalrib 206, of which only one end is visible, are arranged inside thehalf-cover 184 to stiffen the latter.

A plate 208 is arranged at the bottom of the half-cover 184 to enablecorrect positioning of the electronic module protected by the two metalhalf-shells.

It should be noted that the top half-cover 182 has the same arrangementsas those described for the half-cover 184.

The detector activation device 100 cannot be directly handled by theuser for leak-tightness reasons and it is accessible to the user througha thinned zone 210 provided in the top half-cover 182 and which isdesigned to be distorted locally and made to press in under the user'sfinger pressure and return to its initial position when the pressure isno longer exerted.

According to an alternative embodiment, the thinned zone is replaced byan added button created in a flexible material, which the user will haveaccess to and which will be attached to the half-cover 182, for exampleby gluing, so as to ensure the leak-tightness and not to have zonescapable of causing dirt incrustation.

It may be noted that the case 180 enclosing the electronic module 32,and the axial extensions 170 and 172 of this case have external surfacesenabling them to be easily disinfected/sterilized and the forms of thisexternal surface are of a kind not to encourage dirt incrustation.

Furthermore, the external surface of the case and its axial extensions170, 172 is drip-proof to prevent the case interior from beingcontaminated.

The dental radiology apparatus according to the invention thus has aparticularly simple and reliable design. The video signal supplied tothe processing and display unit 54 has very high quality as thedetector's signal-to-noise ratio has been considerably improved comparedwith the prior art.

Other alternative embodiments within the capacity of those skilled inthe art can also be envisaged for the various aspects of the inventionthat have just been described.

The invention claimed is:
 1. A dental radiology apparatus including anintraoral sensor adapted to receive x-rays that have passed through atleast one tooth, the sensor comprising: an x-ray to visible radiationconverter; a detector comprising an active pixel array having biCMOStechnology and converting the visible radiation thus converted into atleast one analog electrical signal; a generator of a sampling signalsynchronized with the at least one analog electrical signal and adaptedfor the later conversion of the at least one analog electrical signalinto a digital signal; and a signal generator capable of generating,based on one analog electrical signal from the detector, twodifferential analog electrical signals.
 2. The dental radiologyapparatus according to claim 1 comprising: an electronic module remotefrom the sensor; and a link between the electronic module and the sensorfor simultaneous and in-phase transmission of the at least one analogelectrical signal and of the sampling signal.
 3. The dental radiologyapparatus according to claim 2, wherein the electronic module comprisesan analog-digital converter for converting the at least one analogelectrical signal into one digital signal based on the sampling signal.4. The dental radiology apparatus according to claim 2, wherein the linkbetween the electronic module and the sensor is a wire link.
 5. Thedental radiology apparatus according to claim 1 wherein the sensorcomprises a sequencer that is capable of generating several controlsignals of the active pixel array and which includes the sampling signalgenerator.
 6. A dental radiology apparatus including an intraoral sensoradapted to receive x-rays that have passed through at least one tooth,the sensor comprising: an x-ray to visible radiation converter; adetector comprising an active pixel array having biCMOS technology andconverting the visible radiation thus converted into at least one analogelectrical signal; a generator of a sampling signal synchronized withthe at least one analog electrical signal and adapted for the laterconversion of the at least one analog electrical signal into a digitalsignal; an electronic module remote from the sensor; a link between theelectronic module and the sensor for simultaneous and in-phasetransmission of the at least one analog electrical signal and of thesampling signal; and a signal generator capable of generating, based onone analog electrical signal from the detector, two differential analogelectrical signals, wherein the signal generator is integrated into thesensor, and wherein the link ensures the simultaneous and in-phasetransmission of the two differential analog electrical signals and thesampling signal.
 7. A signal processing method for a dental radiologyapparatus including an intraoral sensor adapted to receive x-rays thathave passed through at least one tooth, the method comprising stepsperformed in the sensor: receiving x-rays having passed through at leastone tooth; conversing the received x-rays into visible radiation;transforming the visible radiation thus converted into at least oneanalog electrical signal by an active pixel array produced using biCMOStechnology; generating a sampling signal synchronized with the at leastone analog electrical signal and which is intended for the laterconversion of the at least one analog electrical signal into a digitalsignal; simultaneously transmitting the in-phase signals of the at leastone analog electrical signal and the sampling signal to an electronicmodule remote from the sensor; and generating, based on one analogelectrical signal from the array, two differential analog electricalsignals.
 8. The signal processing method according to claim 7 furthercomprising an analog-digital conversion step of the at least one analogelectrical signal into one digital signal based on the sampling signal.9. The signal processing method according to claim 8 wherein theconversion step is performed in the electronic module.
 10. The signalprocessing method according to claim 7 wherein the transmitting isperformed by means of a wire link.
 11. The signal processing methodaccording to claim 7 wherein the generating step of the two differentialanalog electrical signals is performed before the simultaneoustransmission with the sampling signal.